1. Field of the Invention
The present invention relates to a distributor for an internal combustion engine. More particularly, the present invention pertains to an improvement in a distributor for an internal combustion engine which is designed to make it possible to generate a cylinder discriminating signal having a reduced width and also to correct the mass imbalance of the rotator.
2. Description of the Related Art
FIG. 5 shows a conventional distributor for an internal combustion engine. In the figure, the reference numeral 1 denotes a distributor housing, 2 a cap, 3 a rotary shaft rotated synchronously with the internal combustion engine, 4 a reluctor for generating a cylinder discriminating signal which is rotated together with the rotary shaft 3 (hereinafter referred to as "cylinder discriminating reluctor"), 5 a sensor disposed to face the reluctor 4 so as to generate a cylinder discriminating signal when the rotary shaft 3 is rotated, 9 a reluctor for detecting ignition timing (hereinafter referred to as "ignition timing reluctor"), 10 a stator constituting a part of the magnetic circuit of the reluctor 9, 6 a magnet signal type generator for generating an ignition signal for each of the cylinders, 7 an ignition timing control unit for controlling the ignition signal generated from the magnet signal type generator 6 on the basis of the positional relationship between the reluctor 9 and the stator 10, that is, according to whether or not the reluctor 9 and the stator 10 face each other, 8 a centrifugal spark advance controller, 81 a governor base fixed to the rotary shaft, 82, 83 weights, and 84 a centrifugal spark advance plate. The centrifugal spark advance plate 84 has a substantially rectangular configuration in plan view, as shown in FIG. 6. The reference numeral 11 denotes a spark advance sleeve loosely fitted on the rotary shaft 3. The ignition timing reluctor 9 is attached to the spark advance sleeve 11. The sensor 5 is attached to the outer surface of the cylindrical part of the distributor housing 1 in such a manner that the sensing surface 51 of the sensor 5 is exposed in the housing 1. The cylinder discriminating reluctor 4 is fixed to the governor base 81 of the centrifugal spark advance controller 8. The functional part of the cylinder discriminating reluctor 4 approaches and passes the sensing surface 51 of the sensor 5 when the rotary shaft 3 is rotated together with the reluctor 4.
In the case of a four-cylinder engine, the rotary shaft 3 is rotated one full turn per two full turns of the crankshaft (not shown) of the engine, so that four ignition timing signals and one cylinder discriminating signal are output per one full turn of the shaft 3. A cylinder which is defined as a standard is detected by the cylinder discriminating signal from the sensor 5, and the signal is supplied to a fuel injecting device corresponding to the cylinder so that fuel is injected when the valve of the cylinder is opened. Then, ignition is conducted on the basis of the ignition timing signal for each of the cylinders.
In the above-described conventional distributor, the ignition timing signal IG which is generated by the ignition timing reluctor 9 is advanced relative to the engine crank angle, whereas the cylinder discriminating signal G generated by the cylinder discriminating reluctor 4 is not advanced, and therefore, in order to detect a cylinder by means of the signal G overlapping the signal IG, the width .theta..sub.A of the signal G must be greater than the entire range of spark advance .theta., as shown in FIG. 7. For this reason, the width of the functional part of the cylinder discriminating reluctor 4 must be as large as .theta..sub.A, as shown in FIG. 4b. Accordingly, the width of the signal generated by the combination of the cylinder discriminating reluctor 4 and the sensor 5 is relatively wide, and the width .theta..sub.A of the cylinder discriminating reluctor 4 is correspondingly wide, which leads to an increase in the amount of mass imbalance during rotation. Under these circumstances, the prior art suffers from the problems of lowered performance and increases in wear at the bearing portions. Further, since rivets 85 are employed to secure the cylinder discriminating reluctor 4 to the governor base 81, the number of required parts is disadvantageously large. The imbalance of the rotator due to the functional part of the cylinder discriminating reluctor hinders smooth rotation of the spark advance sleeve 11 supporting the rotator of the distributor, which has an adverse effect on the centrifugal spark advance characteristics.